Chromosome I ofTriturus cristatusis readily distinguished after Giemsa C-banding by the heterochromatic region on its long arm. The heteromorphic banding pattern within this region reported previously was found sporadically but not reproducibly. Mortality of half the tailbud embryos from artificial spawnings is confirmed and is probably true for naturally spawned eggs raised in the laboratory, but the survivors often show an unequal sex ratio. These results suggest crested newts have evolved from a genotypic to an environmental control of sex determination, so that chromosome I may be considered as a relict sex chromosome.